Prepa rati on and molecular rearran ge ment of 2a, 3a-epoxy lup an-1-one catalysed by boro n trifluoride and by ultra vio let irrad iati on+

Using lupeol 7 as lead compound 2a. 3a -epoxy lu pan-1-one 11 has been sy nth es ise d by a sequ ence of reacti ons. Boron trinuoride ca talysed molecular rea rran gement of II in benze ne yie lds 2-formyi-A-nor- lupan-1 -onc IS (enol ized). Same rearrangement is also achieved in dioxane under ph otolyti c condition. House and Watson 1 have observed that cyclic epoxy ketones of th e type (l:n> I ) in the presence of boron tri lluoride-etherate undergo molec ular re arran ge ment (C hart 1) with reduction in ring size of ketones and produce th e keto aldehydes 2. L ater. Kartha and Chakravarti} studied the ac tion of boron trifluoride on some sesquiterpene epoxy ke tones and epox ides and fnund th at in each case an aldehyde was formed by contracti on of a six-membered ring to a five­ membered one. Ganguly et. a/. 3 c:.ll·;ied out BF3catalysed rearrangement of I a. 2a-epoxy lupan-3-one 3 and obtained th e product I - methyl-2a-hydroxy­ lup-l ( I O)en-3-one 4. Here, most probably due to th e presence of a neopentyl system adjacent to th e epoxy ketone sys tem, methyl migration occulTed instead of ring contrac ti on. In con trast. Chattetjee et. a /. 4 also stud ied the sa me rearrangement on th e same substrate 3 and report ed the formation of th e nor-ketone 5, presumably formed by the elimination of formyl group from the initial prod uct. 2-formyl cyclopentanone 6. I n this note we wish to repo rt first the partial sy nth es is of the: isomeri c epoxy ke tone 11 possessing a neo pen tyl sys tem adj acen t to th e epoxy ketone moiety and th en the molec ul ar rearran gement of 11 induced by BF3-etherate as well as induced by ultraviolet irradiat ion to give 2-fonnyi-Anor-lu pan-1one 15.